On October 13, 2015, plant owners announced that it would close by June 2019, citing "market conditions and increased costs," which would have included tens of millions of dollars of necessary safety upgrades.[3]

On April 11, 1986, a recurring equipment problem forced emergency shutdown of the plant.

Pilgrim keeps its spent nuclear fuel in an on-site storage pool, waiting for federal direction on the correct disposal process. The Yucca Mountain site in Nevada was being considered for this purpose until its deselection in 2009.

Pilgrim's original license to operate would have expired in 2012. In 2006, Entergy filed an application for an extended operating license (until 2032) with the Nuclear Regulatory Commission.[4] In May 2012, the NRC approved the 20-year extension; NRC chairman Gregory Jaczko was the lone dissenting vote.[5]

Opposition to Pilgrim's license extension came mainly from Pilgrim Watch, a local group which filed numerous legal and procedural challenges. The state attorney general has also raised questions about, among other issues, the possible danger posed by storage of spent nuclear fuel at the Plymouth site.[6]

In July 2013, the plant had to reduce output during a heat wave despite very high electricity demand, because the temperature of water drawn from Cape Cod Bay exceeded 75 °F, the limit set by the NRC.[8]

On August 22, 2013, with the plant online at 98% power, all three of the plant's main feedwater pumps tripped causing a drop of the reactor water level. The reactor subsequently tripped. The loss of feedwater and sudden trip from the high power level caused the reactor water level to drop below -46 inches. After passing this point, the emergency core cooling system automatically activated. The RCIC and HPCI systems promptly restored the reactor water level to normal. The cause of the electrical trip to the feedwater pumps is under investigation.

On January 27, 2015, the plant underwent a storm-induced unplanned shutdown.[9]

The Nuclear Regulatory Commission defines two emergency planning zones around nuclear power plants: a plume exposure pathway zone with a radius of 10 miles (16 km), concerned primarily with exposure to, and inhalation of, airborne radioactive contamination, and an ingestion pathway zone of about 50 miles (80 km), concerned primarily with ingestion of food and liquid contaminated by radioactivity.[10]

The 2010 U.S. population within 10 miles (16 km) of Pilgrim was 75,835, an increase of 40.5 percent in a decade, according to an analysis of U.S. Census data for msnbc.com. The 2010 U.S. population within 50 miles (80 km) was 4,737,792, an increase of 10.2 percent since 2000. Cities within 50 miles include Boston (35 miles to city center).[11]

PNPS operates a single reactor unit with a boiling water reactor and a steam turbine generator. The cooling and service water systems operate as a once-through cooling system, with Cape Cod Bay being the water source. The water is circulated in the plant's heat exchanger in the same manner as any fossil-fuel powered power plant, using the seawater to remove heat from primary coolant away from sources of radioactive contamination. Approximately 480 million gallons of seawater is withdrawn daily from the bay through an intake embayment formed by two breakwaters, and is then re-deposited into the bay causing a change in temperature at peak times (ΔT) of 3 °C (5.4 °F).[12]

During this process, the greatest environmental impact to the bay occurs through impingement and entrainment (I&E) of sea organisms and species. Entrainment occurs when small aquatic life forms are carried into and through the cooling system during water withdrawals. Impingement occurs when organisms are trapped against cooling water intake screens or racks by force of moving water.[12]

PNPS has been regularly monitoring I&E levels since 1974. They have reported I&E losses of millions of aquatic organisms each year. The EPA evaluated all species known to be impinged and entrained by the facility, including commercial, recreational, and forage fish species. Based on information provided in facility I&E monitoring reports, approximately 68 species have been identified in I&E collections since 1974, and 26 of these have commercial or recreational value.[13]

During the license renewal process, the Nuclear Regulatory Commission found that the significance of the potential environmental impacts of renewal would be small, with the exception of marine aquatic resources. Due to I&E, the continued operation of the cooling water system would rarely have impact on the local winter flounder (Pseudopleuronectes americanus) population, and the Jones River population of rainbow smelt, and cumulative impacts on other marine aquatic species would be small to moderate.[13]

After the aquatic organisms are impinged into the cooling system, they are discharged back into the bay as sediment. The resulting shadow effect kills plant and animal life around reactor discharge systems by curtailing the light and oxygen they need to survive;[14] however, the intake and discharge canals remain a popular and lucrative local recreational fishing spot for local residents.[15]

The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at Pilgrim was 1 in 14,493, according to an NRC study published in August 2010.[16][17]